Approximately one in 5000 males in human population suffers from coagulation disorder, hemophilia A. This disease is primarily caused by deficiency in the factor VIII gene located in the X-chromosome and is difficult to treat by conventional medicine. Current treatment of hemophilia A by intravenous infusion of factor VIII concentrates is very costly and has a potential side effect of developing inhibitors. Gene therapy, on the other hand, can potentially prevent these limitations of current treatments. Although recombinant adeno-associated virus (rAAV) vectors are promising for deliver factor VIII gene, applying AAV vector technology to Hemophilia A gene therapy lagged behind other genetic diseases because of this size constraint (limited to ~5kb) and inefficient secretion of factor VIII protein. To improve factor VIII gene delivery utilizing rAAV vectors, we will develop a novel human factor VIII molecules with enhanced expression and secretion. The specific aims for this proposal are: 1). To develop a human factor VIII molecule with improved secretion and expression; 2). To develop a human factor VIII molecule with enhanced specific activity with minimal amino acid alteration; 3). To optimize the AAV factor VIII packaging and expression cassette and carry out preclinical studies in Hemophilia Animal Model. The success of this proposal may lead to a clinical trial of hemophilia A using AAV vectors.